This invention relates to a helical waveguide to rectangular waveguide coupler and more particularly to the input and output coupler to the helical slow-wave structure of the traveling wave tube.
This invention also relates to the method matching the impedance of the coupler to that of the helical slow-wave structure to provide an input or output impedance which matches the source or load impedance, respectively, coupled to the traveling wave tube.
The desirability of a helical waveguide for providing a slow wave structure has been recognized for many years. The structure of the helical waveguide of this invention consists of half of a rectangular center ridge waveguide wound around in a spiral with a hole down the center for an electron beam. The fundamental mode of propagation of the waveguide is effectively slowed relative to the axial movement of electrons by causing the propagating RF energy to follow the spiral pathway.
Although conceptually simple in design, a problem is how to make such a helical waveguide structure and its coupler, especially for high frequency tubes where the waveguide dimensions are measured in the hundredths of inches.